The invention relates to velocity determination by correlation of geomagnetic fields and more particularly to two magnetic sensors mounted in displaced locations on a moving vehicle each providing geomagnetic field related signals to a correlator for determining the vehicle ground speed.
In the field of velocity measurement, it has been the general practice to employ Doppler velocity sensor devices to provide velocity data relative to ground or water for navigation and flight control purposes. Although such devices serve the purposes, they have not proved entirely satisfactory under all conditions of service. Difficulties have been experienced such as measurement errors and frequent loss of signals when flying over water, poor dynamic response when measuring changes in velocity, and the compromising of covert activity due to detection of radiated energy. Additionally, although electromagnetic log devices used exclusively on ships and submarines provide an independent source of own ship velocity reference for damping SINS SCHELUR type oscillations, difficulties such as increased sensitivity to hydrodynamic effect, water currents, and altitude are encountered when measuring velocity with respect to water mass.